1. Technical Field of the Invention
The present invention relates generally to photolithography, and more specifically, to dynamic photolithography systems.
2. Description of Related Art
Recently, dynamic photolithography systems have been developed that employ a spatial light modulator (SLM) to define a pattern that is imaged onto a substrate having a photosensitive surface, such as a layer of photoresist. SLMs are electrical devices that include individually controllable light modulation elements (e.g., liquid crystal cells or micromirrors) that define pixels of an image in response to electrical signals. Typically, at small feature sizes (e.g., 5 μm or smaller), there are tens of millions of light modulation elements within an SLM that is not more than a few square centimeters in area. For example, an SLM including an array of 16,384 columns by 606 rows of 3 μm light modulation elements has been proposed for use in transferring such small feature sizes.
With the small SLM size, multiple exposures are generally required to image the entire area of the substrate. Since the image formed by the SLM is easily reconfigurable, it is a relatively simple process to divide the final image into sections, configure the SLM to transfer one of the image sections onto the appropriate area of the substrate surface, shift the relative position of the substrate and SLM and repeat the process for each image section until the entire image is transferred onto the substrate surface.
However, with the large number of light modulation elements, it is impracticable to assume that the SLM will be free from defects. Statistically, there will be at least a few of the tens of millions of light modulation elements of the SLM that are defective. As a result of the multiple imaging process, each defective light modulation element produces N pixel defects on the substrate surface, where N is the number of sections the image is divided into. To limit the number of defects in the transferred image caused by defective light modulation elements, the data can be shifted through the SLM to transfer each image section onto the same portion of the substrate multiple times using different light modulation elements in the SLM, as described in co-pending and commonly assigned U.S. application for patent Ser. No. 10/737,126.
Strobe lines within the SLM provide strobe signals to the light modulation elements to drive the data shifting between the light modulation elements. However, due to the small size and the high aspect ratio (length to width) of SLMs, circuit loading and strobe line resistance limit the strobe frequencies to unacceptably low values, while also introducing significant clock skew across the SLM. In addition, when the strobe lines are configured to run the length of the SLM, failure points or shorts in the strobe lines can render the entire SLM unusable by preventing data shifting through the SLM. Therefore, what is needed is a strobe mechanism to increase the operational frequency of the strobe lines, reduce clock skew and limit damage from strobe line failure in SLMs.